When Jacob asked Joseph to bury him in Canaan rather than Egypt, he did not ask for a simple promise. In (Genesis 47:29) he asked Joseph to "put thy hand under my thigh" — a euphemism the Targum Pseudo-Jonathan preserves directly as "put thy hand on the place of my circumcision."
This is the oldest oath in Torah. Abraham asked Eliezer to swear the same way in (Genesis 24:2) when sending him to find a wife for Isaac. Now Jacob does it with his son. The Targum makes sure the reader cannot miss what is being sworn upon: ot brit, the sign of the covenant.
The Oath That Cannot Be Broken
Why swear on circumcision? The rabbinic answer is that a shevua, an oath, requires something holy to swear upon. The brit milah is the most physically personal mark of the covenant — the place where the Jewish body itself carries the signature of Abraham's promise. An oath sworn on the brit binds not just the word but the flesh of the one swearing.
Jacob was asking Joseph for something enormous: to transport his father's body out of Egypt, through Pharaoh's bureaucracy, across the Sinai, and all the way to the Cave of Machpelah in Hebron. Such a journey would require royal permission, military escort, diplomatic negotiation. A casual promise would not survive all the obstacles. An oath on the brit would.
What Jacob Feared
The Targum, whose traditions are preserved also in <a href='/categories/midrash-rabbah.html'>Midrash Rabbah</a>, hints at the fear behind the oath. Jacob had seen his wife Rachel die on the road and be buried in haste by the wayside (Genesis 35:19). He had seen Egyptian burial customs — mummification, pyramids, gods of the underworld. He refused to be folded into that system. The Cave of Machpelah, where Abraham, Sarah, Isaac, and Rebekah already rested, was the one address in Jacob's universe that mattered for his bones.
An oath on the brit ensured Joseph could not be dissuaded — not by Pharaoh, not by Egyptian mourning ritual, not by the logistical nightmare of the journey. The covenant itself would push him forward.
The Covenant as Contract
The Targum Pseudo-Jonathan, reaching its final form between the 4th and 8th centuries CE, uses this verse to teach something lasting about Jewish commitment. The deepest promises are not made with words only. They are made with the body — with the piece of the body that carries the oldest yes of the people.
The takeaway is a question. What, in your life, is so important that you would swear upon what your body already remembers? Jacob's answer was: my burial. Joseph's answer was: I will do according to thy word.